1. Field of the Invention
The present application relates to products for inhibiting the corrosion of metal articles. More specifically, the present application relates to a vapour phase corrosion inhibitor which can be incorporated into plastic packaging materials.
2. Discussion of Related Art
Corrosion of metal articles has been the subject of a great deal of study. The most widely known form of corrosion is rust which occurs when iron and metals containing iron are exposed to moisture and oxygen in the air. Corrosion is a significant problem during the storage, handling and transportation of corrodible metal articles as it is difficult and impractical to remove oxygen from the atmosphere in which metal articles are packaged.
One of the first techniques for overcoming the problem of corrosion was to coat all the exposed surfaces of corrodible metal articles with a non-corrodible coating such as paint, varnish, grease or the like. This technique is, however, expensive and time consuming.
A more useful and successful system of preventing the corrosion of metal articles is to package the articles with a material containing a vapour phase corrosion inhibitor. Functioning by slowly releasing vapours that contact the surface of the metals, the vapour phase corrosion inhibitors serve to envelope the metal article in a non-corrosive atmosphere and retard the moisture and oxygen present in the atmosphere from attacking the metal surfaces.
Vapour phase corrosion inhibitors may be applied by spraying the entire surface of the metal article to be protected or the metal article itself may be enclosed, packaged or surrounded in or with materials containing volatile corrosion inhibitors.
U.S. Pat. No. 3,443,577 to Shick discloses a method of protecting metal articles from atmospheric corrosion in which the articles are packaged in a material which has been treated with a vapour phase corrosion inhibitor composition consisting essentially of sodium nitrite and sodium phosphate.
U.S. Pat. No. 4,416,701 to Conner discloses a metal corrosion inhibitor which is prepared by adding an alkali metal nitrite, ammonium benzoate, an alkylalkanolamine and a nitrogenous base such as urea, to water. The inhibitor may be applied as a mist of spray to the exposed edges of coiled sheet steel to protect the steel during storage or may be fogged into a shipping container to protect the steel during shipping.
Other vapour phase corrosion inhibitors are disclosed in U.S. Pat. Nos. 4,338,209, 4,349,457, 4,402,747, 4,557,966, 4,963,290, 4,973,448 and 5,303,743.
U.S. Pat. Nos. 5,209,869, 5,320,778, 5,344,589 and 5,422,187, all issued to Miksic, disclose vapour corrosion inhibitor/desiccant formulations. The inhibitors described in these four related patents are selected from formulations comprising anhydrous molybdates mixed with benzotriazole and sodium nitrite or from a formulation comprising amine benzoate, amine nitrates and benzotriazole. These patents disclose that the formulations can be incorporated into permeable capsules or into laminates containing a central metal layer.
There are a number of issues that require addressing when trying to make a vapour corrosion inhibitor that can be incorporated into plastic wrapping materials. Firstly, the right compounds must be identified and then combined in the correct ratios and levels in the plastic in order to give optimal corrosion inhibition. The second issue is to find an inhibitor that is sufficiently volatile to act in the vapour phase at room temperature (approximately 20.degree. C.) but that will not be significantly volatilized under the high temperatures (in excess of 300.degree. C.) normally encountered during processing of plastics. Furthermore, it is important that none of the components decompose under this high temperature.
The third issue to be addressed in preparing a suitable vapour corrosion inhibitor formulation is the question of toxicity. Many of the inhibitor compositions disclosed in the patents described above contain chromates, amines and nitrites. Although these types of compounds are effective corrosion inhibitors, it is known that chromates and combinations including amines and nitrites are deleterious to health.
The final issue is to find a formulation that is economical to produce. A formulation that acts as an effective corrosion inhibitor, is still effective after high temperature processing and is non-toxic may still not be practical if it is too expensive to be used at the required levels.
There is, therefore, a need to provide a vapour phase corrosion inhibitor composition which overcomes the deficiencies associated with known compositions.